Holographic object relay for light field display

ABSTRACT

Relay systems and methods are operable to redirect light corresponding to a light field or holographic object such that imagery generated by a light field or other display is perceived by a viewer without having to address the display itself.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a National Stage Application of InternationalApplication No. PCT/US2019/053918, which claims the benefit of priorityto U.S. Provisional Patent Application No. 62/739,000, entitled“HOLOGRAPHIC OBJECT RELAY FOR LIGHT FIELD DISPLAY,” filed Sep. 28, 2018,which are both herein incorporated by reference in their entirety.

TECHNICAL FIELD

This disclosure generally relates to systems configured for generatinglight corresponding to 2D, 3D, or holographic imagery and furtherconfigured to relay the generated holographic imagery to desiredlocations.

BACKGROUND

Many technologies exist today that are often unfortunately confused withholograms including lenticular printing, Pepper's Ghost, glasses-freestereoscopic displays, horizontal parallax displays, head-mounted VR andAR displays (HMD), and other such illusions generalized as“fauxlography.” These technologies may exhibit some of the desiredproperties of a true holographic display, however, lack the ability tostimulate the human visual sensory response in any sufficient way.

Light field and holographic display is the result of a plurality ofprojections where energy surface locations provide angular, color andintensity information propagated within a viewing volume. Unlike astereoscopic display, the viewed position of the converged energypropagation paths in space do not vary as the viewer moves around theviewing volume and any number of viewers may simultaneously seepropagated objects in real-world space as if it was truly there.

SUMMARY

An embodiment of a holographic display system includes a first display,comprising a light field display configured to project light along a setof projected light paths to form at least a first holographic surfacehaving a first projected depth profile relative to a display screenplane; and a relay system positioned to receive light along the set ofprojected light paths from the light field display and relay thereceived light along a set of relayed light paths such that points onthe first holographic surface are relayed to relayed locations therebyforming a first relayed holographic surface having a first relayed depthprofile relative to a virtual screen plane, the first relayed depthprofile being different from the first projected depth profile. Thelight field display comprises a controller configured to receiveinstructions for accounting for the difference between the firstprojected depth profile and the first relayed depth profile by operatingthe light field display to output projected light such that the firstrelayed depth profile of the first relayed holographic object is thedepth profile intended for a viewer.

An embodiment of a holographic display system includes a first display,comprising a light field display configured to project light along a setof projected light paths to form at least a first holographic surface,the set of projected light paths determined according to a firstfour-dimensional (4D) function defined by the light field display, suchthat each projected light path has a set of positional coordinates andangular coordinates in a first 4D coordinate system defined with respectto a display screen plane. The system also includes a relay systempositioned to receive light along the set of projected light paths fromthe light field display and relay the received light along a set ofrelayed light paths such that points on the first holographic surfaceare relayed to relayed locations thereby forming a first relayedholographic surface, the set of relayed light paths having beendetermined according to a second 4D function defined by the relaysystem, such that each relayed light path has a set of positionalcoordinates and angular coordinates in a second 4D coordinate systemdefined with respect to a virtual screen plane. The light field displaycomprises a controller configured to receive instructions for accountingfor the second 4D function by operating the light field display tooutput projected light according to the first 4D function such that thepositional coordinates and angular coordinates in the second 4Dcoordinate system for each of the set of relayed light paths allow therelayed holographic surface to be presented to a viewer as intended.

An embodiment of a holographic display system includes a light fielddisplay configured to project light along a set of projected light pathsto form at least first and second holographic surfaces in a first depthorder relative to a display screen plane; a relay system positioned toreceive light along the set of projected light paths from the lightfield display and relay the received light along a set of relayed lightpaths such that points on the first and second holographic surfaces arerelayed to relayed locations thereby forming first and second relayedholographic surfaces perceivable in a second depth order relative to avirtual screen plane, the first and second depth orders are reversed;and a corrective optical element disposed in the set of relayed lightpaths, wherein each of the set of relayed light paths has a set ofpositional coordinates and angular coordinates in a four-dimensional(4D) coordinate system, and wherein the corrective optical element isconfigured to reverse the polarity of the angular coordinates of each ofthe first set of relayed light paths such that the first and secondrelayed holographic surfaces are perceivable with a corrected depthorder that is substantially the same as the first depth order.

An embodiment of a holographic display system includes a light fielddisplay configured to project light along a set of projected light pathsto form at least first and second holographic surfaces in a first depthorder relative to a display screen plane; a corrective optical elementdisposed in the set of projected light paths, wherein each of the firstset of projected light paths has a set of positional coordinates andangular coordinates in a four-dimensional (4D) coordinate system, andwherein the corrective optical element is configured to reverse thepolarity of the angular coordinates of each of the set of projectedlight paths, the first and second holographic surfaces have anintermediate depth order that is reversed from the first depth order;and a relay system positioned to receive light along the set ofprojected light paths from the corrective optical element and relay thereceived light along a set of relayed light paths such that points onthe first and second holographic objects are relayed to relayedlocations thereby forming first and second relayed holographic surfacesperceivable in a second depth order relative to a virtual screen plane,the first and second depth orders are the same.

An embodiment of a holographic display system includes a first display,comprising a light field display configured to project light along afirst set of projected light paths to form at least first and secondholographic surfaces having first and second depth profiles,respectively relative to a display screen plane; and a first relaysystem positioned to receive light along the first set of projectedlight paths from the light field display and relay the received lightalong a first set of relayed light paths such that points on the firstand second holographic surfaces are relayed to relayed locations therebyforming first and second relayed holographic surfaces having first andsecond relayed depth profiles, respectively, relative to a virtualscreen plane.

An embodiment of a holographic display system includes a first display,comprising a light field display configured to project light along afirst set of projected light paths to form at least a first holographicsurfaces having a first depth profile relative to a display screenplane; a first relay system positioned to receive light along the firstset of projected light paths from the light field display and relay thereceived light along a first set of relayed light paths such that pointson the first holographic surface are relayed to relayed locationsthereby forming a first relayed holographic surface having a firstrelayed depth profile relative to a virtual screen plane; and a secondrelay system positioned to receive light from the first relay systemalong the first set of relayed light paths and relay the received lightalong a second set of relayed light paths such that points on the firstrelayed holographic surface are further relayed to new relayedlocations, thereby forming a second relayed holographic surface having asecond relayed depth profiles, respectively, relative to a new virtualscreen plane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an embodiment of a system configured to relay aholographic surface projected by a light field display using a beamsplitter and an image retroreflector;

FIG. 1B illustrates an embodiment of a system configured to relay aholographic surface projected by a light field display using a beamsplitter and a plurality of image retroreflectors;

FIG. 2A illustrates an embodiment of a corrective optical elementconfigured to reverse the polarity of U-V angular coordinates in afour-dimensional (4D) coordinate system;

FIG. 2B illustrates a top-level view of a waveguide placed over a numberof illumination source pixels in the U-V plane;

FIG. 2C illustrates a side view of the embodiment shown in FIG. 2B inthe U-Z plane with a thin lens as the waveguide;

FIG. 3A illustrates an embodiment of a holographic display systemsimilar to the system shown in FIG. 1A, in which the beam splitter andimage retroreflector have been replaced by a transmissive reflector;

FIG. 3B illustrates an embodiment of a holographic display system havingmultiple relay systems;

FIG. 3C illustrates another embodiment of a holographic display systemhaving multiple relay systems;

FIG. 4A illustrates a combined view of an embodiment of a dihedralcorner reflector array (DCRA);

FIG. 4B illustrates a side view of an embodiment of transmissivereflector imaging a point source of light;

FIG. 4C illustrates an embodiment of a holographic display system havinga relay system comprising a concave mirror;

FIG. 4D illustrates another embodiment of a holographic display systemhaving a relay system comprising a concave mirror;

FIG. 4E illustrates another embodiment of a holographic display systemhaving a relay system comprising a beam splitter, at least one lens, anda reflector;

FIG. 4F illustrates another embodiment of a holographic display systemhaving a relay system comprising a lens system;

FIG. 5A illustrates an embodiment of an ideal relay system;

FIG. 5B illustrates an embodiment of holographic display system having arelay system configured to relay first and second holographic surfacesprojected by a light field display using a beam splitter and an imageretroreflector;

FIG. 5C illustrates an embodiment of a holographic display system havinga relay system configured to relay first and second holographic surfacesprojected by a light field display using a beam splitter and a concavemirror;

FIG. 5D illustrates an embodiment of correcting the optical effect ofthe relay system shown in FIG. 5C;

FIG. 5E illustrates an embodiment of a holographic display system havinga relay system configured to relay first and second holographic surfacesprojected by a light field display using a beam splitter and a pluralityof concave mirrors;

FIG. 6 illustrates an embodiment of a holographic display system havinga relay system configured to relay first and second holographic surfacesprojected by a light field display using a transmissive reflector;

FIG. 7 illustrates an embodiment of a holographic display system havinga first relay system configured to relay first and second holographicsurfaces projected by a light field display and relay a third surfaceprojected by a second display;

FIG. 8A illustrates an embodiment of a holographic display system havinga second relay system, a plurality of displays;

FIG. 8B illustrates an embodiment using the parallax barrier in FIG. 8Ato perform occlusion handling;

FIG. 8C illustrates an embodiment of a holographic display systemsimilar to that shown in FIG. 8A perceived by a viewer at a differentposition;

FIG. 8D illustrates an embodiment showing an abstraction of the displaysystem shown in FIGS. 8A and 8B;

FIG. 8E illustrates an embodiment of system of FIG. 8D with atransmissive reflector having a conical surface; and

FIG. 8F illustrates an embodiment of system similar to that shown inFIG. 8E with a pyramid-shaped transmissive reflector surface.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an embodiment of a holographic display system including afirst display 1001 comprising a light field display configured toproject light along a set of projected light paths 1036 to form at leasta first holographic surface 1016 having a first projected depth profilerelative to a display screen plane 1021. In an embodiment, the firstholographic surface 1016 may be any surface in a holographic scene, suchas a portion of an object, a face, a background scene, etc. In anembodiment, the projected depth profile of the holographic surface 1016may include a depth perceivable by a viewer (not shown) observing thefirst display 1001 along a normal axis (not shown) of the display 1001.The holographic display system of FIG. 1A also includes a relay system102A positioned to receive light along the first set of projected lightpaths 1036 from the light field display 1001 and relay the receivedlight along a set of relayed light paths 1025A such that points on thefirst holographic surface 1016 are relayed to relayed locations therebyforming a first relayed holographic surface 1018 having a first relayeddepth profile relative to a virtual screen plane 1022. In an embodiment,the virtual screen plane 1022 is oriented at a non-parallel anglerelative to the display screen plane 1021 of the light field display1001. In an embodiment, the virtual screen plane 1022 is oriented at aperpendicular angle relative to the display screen plane 1021 of thelight field display 1001.

In an embodiment, the depth profile of the holographic surface 1016 mayinclude a depth perceivable by a viewer 1050 observing in the directionof the virtual screen plane 1022. As illustrated in FIG. 1 , the firstrelayed depth profile of the relayed holographic surface 1018 isdifferent from the first projected depth profile of the firstholographic surface 1016: first holographic surface 1016 is projected asan off-screen holographic surface while the first relayed holographicsurface 1018 is perceivable by viewer 105 as an in-screen holographicsurface relative to the virtual screen plane 1022.

In an embodiment, the relay system 102A may relay holographic objectsprojected by a light field display 1001 using a beam splitter 101 and animage retroreflector 1006A. In an embodiment, the light field display1001 comprises one or more display devices 1002, having a plurality oflight source locations (not shown), an imaging relay 1003 which may ormay not be present which acts to relay images from the display devicesto an energy surface 1005, and an array of waveguides 1004 which projecteach light source location on the energy surface 1005 into a uniquedirection (u,v) in three dimensional space. The energy surface 1005 maybe a seamless energy surface that has a combined resolution that isgreater than the surface of any individual display device 1002. Examplesof light field display 1001 are described in commonly-owned U.S. Pat.App. Pub. Nos. US2019/0064435, US2018/0356591, 2018/0372926, and U.S.patent application Ser. No. 16/063675, all of which are incorporatedherein by reference for all purpose. Projected light rays 1036 mayconverge at a location 111 on the surface of a holographic object 1016,and then diverge as they approach the beam splitter 101. The beamsplitter 101 may be configured to include a polarizing beam splitter, atransparent, aluminum-coated layer, or at least one dichroic filter. Inan embodiment, the beam splitter 101 may be oriented at a 45 degreeangle relative to the display screen plane 1021 and the retroreflector1006A, and the retroreflector 1006 is oriented orthogonally relative tothe display screen plane 1021. Some fraction of the incident light alongthe projected light path 1036 reflects from the beam splitter 101 towardthe image retroreflector 1006A along a set of reflected light paths1037, while much of the remaining light passes through the beam splitter101 into rays along a set of transmitted light paths 1039A, which maynot contribute to the formation of the relayed holographic object 1018in FIG. 1A. In an embodiment, the retroreflector 1006A may contain afine array of individual reflectors, such as corner reflectors. Theretroreflector 1006A acts to reverse each ray of incident light in theopposite direction from the approach direction, with no significantspatial offset. Rays along light paths 1037 reverse their direction uponreflecting from the retroreflector 1006A, substantially retracing theirapproach angle to the retroreflector 1006A, and some fraction of theirintensities pass through the beam splitter 101 along the set of relayedlight paths 1025A, converging at the location 112 of the holographicobject 1018. In this way, holographic object 1016 projected directly bythe light field display 1001 is relayed to form the relayed holographicobject 1018.

FIG. 1A may have an optional optical element 1041A located between thebeam splitter 101 and the retroreflector 1006A. The relative placementof this optional optical element 1041A is similar to the optionaloptical element 1041A that appears in FIG. 1B. This optical element maybe a polarization controlling element used together with a polarizationbeam splitter 101. If the display 1001 produces only one polarizationstate, then a polarizing beam splitter 101 may be arranged to directalmost all the light of the display toward the retroreflector 1006A,eliminating most of the light rays 1039A which may pass verticallythrough the beam splitter and not contribute to imaging the holographicobject 1018. Using a polarizing beam splitter 101, the light rays 1037are linearly polarized as they approach the optical element 1041A, andare circularly polarized after passing through the optical element1041A, which may include a quarter wave retarder. Upon reflection fromthe retroreflector 1006A, most of the light on rays 1025A may becircularly polarized in the opposite direction, and for this oppositecircular polarization, the return pass through the quarter wave retarderwill result in these light rays converted to a linear polarization thatis rotated 90 degrees relative to the light leaving the beam splitter101 on rays along the reflected light paths 1037. This light has theopposite polarization to the light that was reflected by the beamsplitter 101, so it will pass straight through the beam splitter 101rather than being deflected, and contribute to the imaging ofholographic object 1018. In short, a quarter wave plate optical element1041A placed between the beam splitter 101 and the retroreflector 1006Amay assist in converting the majority of light reflected from the beamsplitter 101 from one linear polarization to the opposite linearpolarization, so that this light is passed by the beam splitter 101 withoptimal efficiency in generating a holographic image, and limited wastedlight.

In cases where the display 1001 produces unpolarized light, about halfof the incident light 1036 on the beam splitter will be directed tolight rays along the set of reflected light paths 1037 toward theretroreflector 1006A, and about half of the incident light will bedirected along a set of transmitted light paths 1039A, in the verticaldirection. This results in a loss of light rays 1039A. In an embodiment,as shown in FIG. 1B, the holographic display system of FIG. 1A mayinclude a relay system 102B that includes an additional retroreflector1006B. In an embodiment, the additional retroreflector 1006B may bedisposed opposite to the display 1001 from the beam splitter 101,symmetric in distance but orthogonal in orientation to retroreflector1006A. FIG. 1B shows a system which relays holographic surfacesprojected by a light field display 1001 using a holographic relay system102B comprised of a beam splitter 101 and two image retroreflectors1006A and 1006B, where each retroreflector reflects rays of incidentlight in the direction reverse of their incident direction. In contrastto FIG. 1A, in which the light rays along the transmitted paths 1039Aare lost, the light rays along the transmitted paths 1039B areretroreflected from retroreflector 1006B in the same way as rays alongthe reflected paths 1037 are retroreflected from retroreflector 1006A.Light rays along transmitted paths 1039B and reflected paths 1037 areretroreflected and converge at the beam splitter 101, and combine toform light rays along the set of relayed paths 1025B, which focus atpoint 112, contributing to the first relayed holographic surface 1018.In an embodiment, the additional retroreflector 1006B and the beamsplitter 101 are aligned such that projected light that was transmittedthrough the beam splitter 101 towards the additional retroreflector isreflected from the additional retroreflector 1006B and further reflectedby the beam splitter 101 along an additional set of relayed light paths1025B towards the virtual display screen 1022, and the set of therelayed light rays 1025A from first retroreflector 1006A and theadditional set of relayed light rays 1025B from the additionalretroreflector 1006B substantially overlap. As discussed in regard tothe optional optical element 1041A shown in FIG. 1A, the optical element1041B may include a quarter wave retarder which may result in a majorityof light rays along the transmitted paths 1039B returning to the beamsplitter 101 with the opposite linear polarization, such that themajority of these light rays will be directed by the beam splitter 101toward the formation of the holographic surface 1018, rather thanstraight through the beam splitter 101 and towards the display 1001. Theoptional optical element 1041B may contain polarization controllingelements, diffractive elements, refractive elements, focusing ordefocusing elements, or any other optical elements.

Referring now to FIGS. 1A and 1B, in an embodiment, the verticaldistance D1 between points such as location 111 on the directlyprojected surface 1016 may be the same as the horizontal distance D1between points such as location 112, which corresponds to location 111,on the relayed holographic surface 1018. The relay system 102A or 102Bmay be configured to relay a plurality of holographic surfacesdistributed around display screen plane 1021, including theout-of-screen surface 1016 on the side 1010 of the screen plane 1021,and surfaces that are projected in-screen on the side 1011 of the screenplane 1021. In the example shown in FIGS. 1A and 1B, the surface 1016 isprojected as an off-screen holographic surface. These holographicsurfaces may be relayed from screen plane 1021 to virtual plane 1022 sothat surfaces 1016 which are out-of-screen for the screen plane 1021appear behind the virtual plane 1022 with respect to a viewer 1050, andsimilarly, so that surfaces that are in-screen for the light fielddisplay 1001, projected on the side 1011 of screen plane 1021, appear infront of the virtual screen plane 1022 with respect to a viewer 1050.For this reason, the depth of holographic surface 1016 flipspolarity—the location 111 of the out-of-screen holographic surface 1016that is furthest away from the display screen plane 1021 is relayed tolocation 112 of the relayed holographic surface 1018 that is furthestfrom the viewer 1050. To account for this reversal of depth, and topresent the observer 1050 with the same view and same depth profile ofthe relayed holographic surface 1016 that an observer of directlyprojected out-of-screen holographic object 1016 would see without theuse of relay system 102B, one approach is to reverse the polarity of theU-V light field coordinates, which are the two angular coordinates inthe 4D light field function with coordinates (X, Y, U, V, convertingprojected light rays 1036 into projected light rays 1013, each of whichhave the opposite slope. This converts out-of-screen holographicprojected surface 1016 into in-screen holographic projected surface 1014with a reversed depth, which will be relayed into relayed holographicsurface 1020. Relayed holographic surface 1020 is out-of-screen relativeto the virtual display plane 1022, and will appear to observer 1050 tohave the same depth profile relative to the virtual screen plane 1022 asprojected object 1016 has relative to the display screen plane 1021.Projected holographic surface 1014 will appear to be depth-reversedrelative to the display screen plane 1021. In summary, to project aholographic surface 1020 for observer 1050 of the virtual screen plane1022, the intended projected holographic surface 1016 with the intendeddepth profile may be rendered for the display screen 1021, and then eachof the U-V angular light field coordinates may be flipped to produce adepth-reversed surface 1014 which appears on the opposite side of thedisplay screen plane 1021 from holographic object 1016, but which isrelayed by relay system 102A or 102B into relayed holographic object1020 with the intended relayed holographic surface and the intendeddepth profile relative to the virtual screen plane 1022. The 4D lightfield coordinate system for (X,Y,U,V) is described in in commonly-ownedU.S. Pat. App. Pub. Nos. US2019/0064435, US2018/0356591, US2018/0372926,and U.S. patent application Ser. No. 16/063,675, which are incorporatedherein by reference and will not be repeated here.

In an embodiment, each of the set of projected light paths 1036 has aset of positional coordinates and angular coordinates in afour-dimensional (4D) coordinate system defined with respect to thedisplay screen plane, and each of the set of relayed light paths 1025A,1025B has a set of positional coordinates and angular coordinates in afour-dimensional (4D) coordinate system defined with respect to thevirtual display plane. As described above, holographic surface 1014 maybe rendered so that the light forming the surface of object 1014 will berelayed as the intended distribution for the relayed surface 1020 whichmay be directly viewed by observer 1050. One way to render holographicsurface 1014 is to first render holographic object 1016, the intendedobject to be shown in absence of relay systems 102A or 102B, and thenreversed in polarity its U-V angular coordinates. This reversal of U-Vcoordinates may result in holographic object 1014 being projectedinstead of object 1016, which may be relayed to the intended location ofthe holographic object 1020. The U-V polarity reversal may be done witha corrective optic element, as summarized below in reference to FIG. 2A,or using an adjustment in the 4D light field coordinates, as summarizedbelow in reference to FIGS. 2B and 2C.

FIG. 2A shows an embodiment of a corrective optical element which actsto reverse the polarity of U-V angular light field coordinates. Twosubstantially identical rows of lenses 201, 202 are placed side-by-side.The rows of lenses 201 and 202 has a focal length f, and are orientedparallel to one another, with a spacing of twice the focal length f, sothat their focal planes overlap at virtual plane 203, and so that lenseson opposite sides of virtual plane 203, such as 213 and 214, share acommon optical axis 204. Incoming parallel light rays 211 are incidenton lens 213 with an incident angle to the optical axis 204 of θ in theU-Z plane, and ϕ in the V-Z plane. The light rays 211 are focused bylens 213 onto the focal plane 203, and then diverge toward lens 214,which refracts the rays into parallel rays 212. Parallel rays 212 leave20 with the reversed polarity angles of −θ with respect to the opticalaxis 204 in the U-Z plane, and −ϕ with respect to the optical axis 204in the V-Z plane, resulting in a direction that has been reversedrelative to the incident direction of parallel rays 211. This relaysystem may be placed above the screen plane 1021 in the projected lightpaths 1036 or in the relayed light paths 1025A, 1025B in FIGS. 1A and 1Bin order to reverse the polarity of U-V coordinates for projectedholographic surfaces or relayed holographic surfaces, respectively.

In an embodiment, the light field display 1001 may include a controller190, as shown in FIGS. 1A and 1B, configured to receive instructions foraccounting for the difference between the first projected depth profileand the first relayed depth profile by operating the light field display1001 to output projected light such that the first relayed depth profileof the first relayed holographic object is the depth profile intendedfor a viewer 1050. FIG. 2B shows a top-level view of a waveguide 221 ofthe light field display 1001 placed over a number of illumination sourcepixels 222 in the U-V plane, including a row of pixels at V=0, a columnof pixels at U=0, and individual pixels 223 and 224. In an embodiment,the waveguide 221 allows light from the pixels 222 to be projected alongthe set of projected light paths 1036 where each projected light path1036 has set of positional coordinates (X, Y) and angular coordinates(U,V) in a four-dimensional (4D) coordinate system. In order to reversethe polarity of the U-V coordinates, and create holographic object 1014from a light field rendered for holographic object 1016 in FIGS. 1A and1B, one would exchange the polarity of the U and V coordinates as shownin the diagram, so that a pixel 224 with −U and +V coordinates wouldswap places with a pixel 223 with +U and −V coordinates. All otherpixels would swap positions as indicated, with the exception of U,V=0,0,which stays in place.

FIG. 2C shows a side view of the embodiment shown in FIG. 2B in the U-Zplane with a thin lens as the waveguide 221. The two pixels located atthe minimum and maximum U coordinates for a row of pixels 222 at V=0 areswapped. The result is that the intensity and color of projected raysfrom the pixels at the minimum U, 231, and the maximum U, 232, swapplaces.

FIGS. 3A shows an embodiment of a holographic system which is similar tothe configuration shown in FIGS. 1A, except that the relay system 102Ashown in FIG. 1A comprised of the beam splitter 101 and imageretroreflector 1006A has been replaced by a relay system which iscomprised of a single transmissive reflector 301 positioned to receivelight along the set of projected light paths 1036 and direct thereceived light along the set of relayed light paths 1026. In anembodiment, the transmissive reflector 301 internally reflects a portionof the received light among a plurality of internal reflective surfaces(shown as 401, 402 in FIG. 4A, described below) of the transmissivereflector 301 and output light along the set of relayed light paths 1026towards the virtual screen plane 1022 in a first direction. An exampleof the transmissive reflector 301 may be a dihedral corner reflectorarray (DCRA), which is an optical imaging element composed of aplurality of dihedral corner reflectors, which may be realized as twothin layers of closely-spaced parallel mirror planes, oriented so theplanes are orthogonal to one another as shown in FIG. 4A. Anotherexample is a corner reflector micro mirror array. Projected light rays1036 may converge at a location 111 on the surface of a holographicsurface 1016, and then diverge as they approach the transmissivereflector 301. The transmissive reflector 301 internally reflects thediverging rays 1036 such that they exit the other side of 301 as raysalong the relayed paths 1026 and converge at location 112 of relayedholographic surface 1018. This may be accomplished within thetransmissive reflector 301 through a sequence of two reflections asshown in FIG. 4A. In this way, holographic surface 1016 projecteddirectly by the light field display 101 is relayed to form relayedholographic surface 1018.

FIG. 4A shows an assembled view of an embodiment of the detailedstructure of a DCRA 401, as well as the path of a light ray that passesthrough the DCRA 41. In an embodiment, the DCRA is constructed of twolayers 406 and 407 of closely-spaced reflective planes that are parallelbut offset in a first dimension and the direction of the reflectiveplanes 401 in layer 406 are oriented orthogonally to the direction ofthe reflective planes 402 in layer 407 in as second dimension.Reflective surfaces 401 and 402 may be mirrored surfaces. An incidentlight ray 404 reflects some of its energy into reflected light ray 414as it passes through the external surface (shown as 430 in FIG. 4B) ofthe transmissive reflector. Light ray 404 has one component of itsmomentum reversed upon the first reflective surface 401 at location 410,and then has a substantially orthogonal component of momentum reversedupon a second reflection at point 411 from the second reflective surface402.

FIG. 4B shows a side view of an embodiment of transmissive reflector421, which may be a DCRA, imaging a point source of light 422 located adistance D from transmissive reflector 421. The transmissive reflector421 is aligned parallel to the X-Y plane. Each of the rays of light 423from the point source 422 has its X and Y momentum components reversedby transmissive reflector 421, so that the light rays 424 that exit 421converge at image point 425, a distance D from transmissive reflector421. A portion of the light rays 423 reflect off of the externalsurfaces 430 of the transmissive reflector 421, creating reflected lightrays 433.

Turning now to FIGS. 3B and 3C, it is possible to use a configurationwith more than one relay to relay holographic surfaces. If a holographicsurface is relayed twice, then the depth reversal of the holographicobject that may occur with the first relay may be undone with the secondrelay. This is generally true for holographic surfaces that are relayedby an even number of holographic relays. FIG. 3B shows a light fielddisplay system comprised of at least a first light field display 1001A,and two relay systems 130 and 140 which together relay at least a firstprojected holographic surface to a final relay location. In theembodiment shown in FIG. 3B, holographic surfaces 121A and 122A areprojected around the light field display screen plane 1021A and relayedto final relayed locations 121C and 122C around a virtual display plane1022B, with no depth reversal. Also shown in FIG. 3B is an optionalsecond light field display 1001B, which may project an image surface123A. In place of the second light field display 1001B, the surface 123Amay be the surface of a real-world object, the image of which will becombined with holographic surfaces 121A and 122A by the beam splitter101 and relayed by the pair of relay systems 130 and 140 to imageposition 123C, with no depth reversal. The holographic surfaces and theimage of the real-world object are combined and relayed together to anew relayed location, allowing the holographic surfaces and thereal-world object to be displayed together free of a physical displayplane.

In FIG. 3B, both relay systems 130 and 140 include transmissivereflectors 301A and 301B, respectively, but either one of these relayscould also be comprised of a beam splitter and a retroreflector likerelay 102A shown in FIG. 1A. The holographic surfaces 121A and 122A areformed with light along a set of projected light paths 131A and 132Afrom light field display 1001A, and some fraction of light along the setof projected light paths are transmitted straight through the beamsplitter 101. The beam splitter may be any beam splitter disclosed inthe present disclosure. Projected light along the set of projected lightpaths 131A and 132A are relayed by first relay system 130 along a firstset of relayed light paths 131B and 132B which form depth-reversed firstand second relayed holographic surfaces 121B and 122B around firstvirtual screen plane 1022A, respectively. Light along the first set ofrelayed light paths 131B and 132B are relayed by the second relay system140 along a second set of relayed light paths 131C and 132C, which formthird and fourth related holographic surfaces 121C and 122C, notdepth-reversed, around a new virtual screen plane 1022B. Relayedholographic objects 121C and 122C should have the same depth profilerelative to screen plane 1022B as the depth profile of source projectedsurfaces 121A and 122A, respectively.

Image surface 123A is either the surface of a real-world object, or aholographic surface projected by the optional second light field display1001B with a depth profile with respect to the screen plane 1021B of thelight field display 1001B. A portion of light along input paths 133Yfrom surface 123A are reflected by the beam splitter 101 into projectedlight paths 133A, while the other portion passes through the beamsplitter 101 along a set of transmitted paths 133Z. The transmissivereflector 301A of relay system 130 has reflective surfaces 430, and someof the incident light along the projected paths 133A reflects into lightpaths 143A (and this is true for light along the projected paths 131Aand 132A, but this is not shown in FIG. 3B). A portion of light alongprojected paths 133A from the object 123A are relayed by first relaysystem 130 to relayed light paths 133B of a first set of relayed lightpaths 131B, 132B, and 133B. The light paths 133B form depth-reversedimage 123B. Some of the light along the relayed light paths 133B reflectfrom the surface of transmissive reflector 301B of relay system 140along reflected paths 143B (this is also true for incident light alongrelayed light paths 131B and 132B, but these reflections from thesurface of transmissive reflector 301B are not shown FIG. 3B). The otherportion of light along the relayed light paths 133B are relayed a secondtime by second relay system 140 to relayed light paths 133C of a secondset of relayed light paths 121C, 132C, and 133C. The relayed light paths133C form relayed surface 123C, not depth-reversed, which is either animage of a real-world object 123A, or a relayed holographic surface123A, wherein relayed surface 123C has the same depth profile toobserver 1050 as the source projected holographic surface 123A has withrespect to display screen plane 1021B. The virtual screen plane relayedfrom display screen plane 1021B is virtual screen plane 1022C. Firstobserver 1050 will see either two relayed holographic surfaces 121C and122C, and a holographic image 123C of real-world surface 123A, or threerelayed holographic objects 121C, 122C, and 123C. In the configurationshown in FIG. 3B, by using the beam splitter 101 with the second lightfield display 1001B in place, the holographic content from two lightfield displays may be superimposed into the same space around secondvirtual screen 1022B, without depth reversal, allowing for an increasein the depth range for displaying holographic objects that exceeds thedepth range of either of the individual light field displays 1001A or1001B. Note that each display 1001A and 1001B may produce holographicobjects in a holographic object volume in the neighborhood ofcorresponding display screen planes 1021A and 1021B, respectively. Theseholographic object volumes are relayed to virtual screen plane 1022Bcorresponding to display screen 1021A and virtual screen plane 1022Ccorresponding to display screen 1021B. The amount of separation betweenvirtual screen planes 1022B and 1022C is dependent on the difference ina first distance between display 1001A from the transmissive reflector301A, and a second distance between display 1001B and the transmissivereflector 301A. If these distances are the same, then the virtual screenplanes 1022B and 1022C will overlap. Also note that since the proximityof either light field display 1001A or 1001B from the beam splitter 101may be adjusted, the relayed holographic object volumes in theneighborhood of the virtual screen planes 1022B and 1022C may containeither one large or two smaller but separated regions for display ofholographic objects that is tunable for a given application. In theevent that the relayed holographic object volumes overlap, then acombined relayed holographic object volume larger than the holographicobject volume of either of the individual displays may be achieved.Similarly, if a real-world surface 123A is used in place of aholographic surface 123A, the relative positioning of relayedholographic objects 121C and 122C with the holographic image 123C fromthe real-world object 123A may be adjusted and customized to anyapplication. Note that this discussion about variable separation betweenscreen planes 1022B and 1022C can also be applied to the case when onlyone relay is used, such as 130.

FIG. 3C shows the same configuration shown in FIG. 3B, but the lightthat reflects from the second transmissive reflector 301B of the secondrelay system 140 along the set of reflected paths 141B, 142B, and 143Bare shown being received by a second observer 1051. The numbering inFIG. 3B applies to FIG. 3C. Light along the first set of relayed lightpaths 131B and 132B from depth-reversed relayed holographic objects 121Band 122B are reflected into reflected light paths 141B and 142B,respectively, and may, in an embodiment, pass through a correctiveoptical element placed at plane 137. The corrective optical element maybe similar to that shown in FIG. 2A, acting to reverse the polarity ofthe angular light field coordinates u and v, resulting in the secondobserver 1051 perceiving the relayed holographic surfaces 121C and 122Cwith the same depth profile relative to plane 137 as the depth profileof the source projected surfaces 121A and 122A relative to display plane1021 of light field display 1001A, respectively. In a similar way, theobject 123A, which may be a holographic surface projected by display1001B, or a the surface of a real-world object, produces rays of lightwhich are relayed by relay system 130 along relayed light paths 133Bwhich form depth-reversed image 123B, and are reflected by the surface430 of transmissive reflector 301B into light along the reflected paths143B. The optional corrective optical element placed at 137 justdescribed may also reverse the depth so that second observer 1051 maysee relayed image 123C with the same depth profile as the depth profileof surface 123A. In this way observers 1050 and 1051 will see the sameholographic images in the same locations.

As previously described, if first observer 1050 sees depth-correctrelayed holographic images 121C, 122C, and 123C, then the correspondinglight along paths 141B, 142B, and 143B approaching plane 137 on its wayto second observer 1051 will be of depth-reversed images 121B, 122B, and123B. Instead of placing corrective optics at plane 137, it is possibleto instead use a third relay system (not shown) to reverse the depths ofthese depth-reversed images 121B, 122B, and 123B. One drawback to thismethod is the fact that with an additional relay (not shown) now thesecond observer 1051 (located in a different position to receive lightfrom the additional relay, not shown) of the relayed images will not seethese relayed images at the same locations as holographic images 121C,122C, and 123C perceived by the first observer 1050.

It is possible to use other focusing optical elements, defocusingoptical elements, mirrored surfaces, or any combination of these torelay a holographic object volume around a light field display plane.FIG. 4C shows an embodiment which uses a curved mirror as a focusingelement in place of a retroreflector to relay a holographic objectvolume without depth reversal. FIG. 4C shows an orthographic view of atriangular surface being imaged using a holographic relay system 460comprised of both a beam splitter 462 and a concave mirror 452, wherethe surface is on the optical axis 453. In an embodiment, the concavemirror 452 may be spherical, parabolic, or some other shape. The beamsplitter 462 may be any beam splitter described herein. The triangularsurface 461 is placed on a vertical axis 454 which is orthogonal to thehorizontal optical axis 453. The center of the curvature of the mirrorC, at 451, is distance D1 away from the beam splitter. The point C′ 441is also the same distance D1 away from the beam splitter, on thevertical optical axis 454. A portion of light leaving the point C′ 441along a set of projected light paths 465 will reflect from the beamsplitter 462 into light rays along a set of reflected light paths 466incident on the mirror 452. The concave mirror 452 and the beam splitter462 are aligned such that a portion of light 466 reflected from the beamsplitter 462 towards the concave mirror 452 is reflected and focusedfrom the concave mirror 452 back through the beam splitter 462 along aset of relayed light paths 467 that extend along a return directionsubstantially opposite to the set of reflected light paths 466. Lightalong the relayed paths 467 may be relayed through point C 451 towardsthe virtual screen plane 469. Surface 461 could be a real surface, or aholographic surface projected by a LF display 463. Similarly, light raysalong projected paths 471 from surface 461 will reflect from the beamsplitter 462 into reflected light paths 472, which reflect from theconcave mirror 452, and some of the return light 473 will pass throughthe beam splitter 462 and along relayed light paths 474 which convergeto contribute to forming an relayed image 457 of the surface 461 viewedby observer 450. The optional optical layer 464 may containpolarization-controlling optics, lens elements, diffractive optics,refractive optics, or the like. In one embodiment, as described abovefor FIG. 3A, optical layer 464 is a quarter wave retarder which mayconvert linearly polarized light into circularly polarized light, andvice-versa. If a polarization beam splitter 462 is used, the lightleaving the beam splitter 462 on the reflected light paths 472 islinearly polarized in a first state. Rays along the reflected lightpaths 472 may be converted from the first state of linear polarizationto a circular polarization which is converted to the opposite circularpolarization upon reflection by the mirror 452, and further converted toa second state of linear polarization orthogonal to the first state bythe quarter wave retarder 464. The result is that rays 473 approachingthe polarization beam splitter 462 will have the opposite linearpolarization as compared to rays along the reflected light path 472leaving the polarization beam splitter 462, and these rays will passthrough the beam splitter 462, contributing to the imaging of therelayed image 457 viewed by viewer 450, rather than being deflected. Inthe configuration shown in FIG. 4C, holographic surfaces projected bythe LF display 463 around the display screen plane 468, which may be thesame as the display surface of the LF display 463, are relayed to bearound the virtual screen plane 469, viewable by an observer 450.

In an embodiment, surfaces in the vicinity of point C′ 441 are relayedinto the vicinity of point C 451. Another feature of this optical systemis that objects that are closer to the beam splitter 462 than point C′441 are imaged to a position further than the point C 451 from the beamsplitter, with magnification, and objects that are further from the beamsplitter 462 than point C′ 441 are imaged to a position closer than thepoint C 451 from the beam splitter, with minification. This means thatthe depth ordering for holographic objects produced in the vicinity ofpoint C′ 441 is respected when they are relayed to point C 451. Themagnification or minification of objects in the vicinity of point C′ 441may be reduced by increasing the radius of curvature of mirror 452and/or making the depth range of the projected holographic objects smallabout point C′ 441 relative to the radius of curvature of the mirror452. While the example illustrated in FIG. 4B shows a spherical mirror,it is possible to use different configurations of mirrors to performimaging, including parabolic-shaped concave mirrors, and even convexmirrors which may be spherical or parabolic for projection of imageswith convergence points behind the mirror (to the right of the mirror452 in FIG. 4C), on the other side of the mirror from the viewer 450.

In some embodiments, the focusing function of the mirror 452 shown inFIG. 4C may be replaced with one or more optical elements such aslenses, mirrors, or some combination of these elements. In oneembodiment, shown in FIG. 4E, the relay system 460 may be replaced by arelay system 470 comprised of a beam splitter, one or more lensesincluding lens 444 and optional lens 445, and a reflector 442 on theopposite side of the one or more lens from the beam splitter 462. Thereflector may be orthogonal to the optical axis 453. The optical axes ofthe one or more lenses may be substantially aligned with optical axis453. In this case, the light rays from holographic object 461 reflectingfrom the beam splitter 462 and toward the reflector 442 would each passthrough the one or more lens, and the one or more lens would provide afocusing function. In one embodiment, a planar reflector is used, andthe focal plane of at least one lens 444 or lens 445 is located at thefocal point of the planar reflector 442. In a different embodiment, thereflector 442 is curved. In another embodiment, the one or more lenses444, 445 are replaced with arrays of much smaller lenses.

In another embodiment, the entire relay system 460 may be replaced witha relay formed of one or more lenses. FIG. 4F shows an embodiment inwhich lens relay system 480, comprised of one or more lenses which relayholographic surface 437 around the screen plane 468 of light fielddisplay 463 to relayed holographic surface 438, replaces relay system460. The one or more lenses including lens 446 and optional lens 447 mayhave a common optical axis that may be substantially aligned with anormal to the display surface 468, along optical axis 454. The one ormore lenses may perform a focusing function which optically relays theregion around the display screen plane 468 to a virtual screen plane 435near the optical axis but on the far side of the one or more lenses fromthe light field display 463. Optical systems with lenses may alsocontain focus points, and magnification or minification of holographicobjects projected by the light field display 463 in the vicinity of thedisplay screen plane 468, much the same as described above for theconfiguration shown in FIG. 4D.

FIG. 4D is an orthogonal view of a holographic surface 488 being relayedto holographic surface 489 using a holographic relay system comprised ofa curved concave mirror 482 and a beam splitter 485, where theholographic surface is offset from the optical axis 483. The point 481is a focal point of the mirror which may be spherical, parabolic, orsome other shape. As drawn, the surface 488 is a holographic surfaceprojected from a light field display 497, but the imaging described herealso works if the surface 488 is a real surface. Light paths 490C and492C are projected at different angles from the light field display 497,and converge to form another vertex of the surface 488. These lightalong projected paths 490C and 492C reflect from the beam splitter 485(with some loss due to passing directly through the beam splitter, whichis not shown) to become light rays along reflected light paths 490D and492D, which then reflect off the surface of the mirror 482 to becomelight rays on relayed paths 490E and 492E, which pass through the beamsplitter (with some loss, which is not shown) and converge again at onevertex of the image 489, helping form the image 489. Light rays alongpaths 491C and 493C are projected at different angles from the lightfield display 497, and converge to form one vertex of the surface 488.These light rays along 491C and 493C reflect from the beam splitter 485(with some loss due to passing directly through the beam splitter, whichis not shown) to become light rays along reflected paths 491D and 493D,which then reflect from the surface of the mirror 482 to become lightrays on relayed paths 491E and 493E, which pass through the beamsplitter (with some loss, not shown) and converge again at one vertex ofthe image 489, helping form the image 489. Light rays along projectedpaths 492C and 493C reflect as light rays along reflected paths 492D and493D from the beam splitter, and pass through the focal point 481 of thecurved mirror 482, turning into rays along relayed paths 492E and 493Ewhich are parallel to the optical axis. Light rays along projected paths490C and 491C reflect from the beam splitter as light rays alongreflected 490D and 491D, respectively, and are parallel to the opticalaxis before reflecting from the curved mirror 482, so their reflectedrays along relayed paths 490E and 491E, respectively, pass through thefocal point 481 of the curved mirror 482. In the configuration shown inFIG. 4D, holographic surfaces projected by the LF display 497 around thescreen plane 498, which may be the same as the display surface of the LFdisplay 497, are relayed to be projected around the virtual screen plane469, viewable by an observer 450.

In an embodiment, light rays along projected paths 490C and 491C in FIG.4D are projected at a normal to the surface of the light field display497, at a single angle, or equivalently, a single value of light fieldangular coordinate, which we assign to be u=0 (u is in the plane of thedrawing—the orthogonal angular light field coordinate v is not discussedin reference to FIG. 4D, but similar comments apply to v as well). Theserays are reflected by the beam splitter 485 into rays along reflectedpaths 490D and 491D, which then reflect from the mirror into rays alongthe relayed paths 490E and 491E. These two light rays, visible to theobserver 450, make different angles θ₁ and θ₂ with a normal 496 to aline 495 parallel with the virtual screen plane 496, and thus contributetwo different values of light field angular coordinate u to the imagingof the relayed holographic surface 489. In other words, despite bothrays having a single value of light field angular coordinate u=0 asprojected by the light field display 497, they have different values ofu at the relayed holographic surface 489, and this u value (orequivalently angle) is dependent in part on the position of the objectrelative to the focal point 481 of the mirror. Also, the two rays alongprojected paths 492C and 493C, projected at light field angularcoordinates (u1 and a u2) from the light field display 497, reflect fromthe beam splitter and the mirror system to become light rays alongrelayed paths 492E and 493E, both parallel to each other and parallel toa normal 496 to the virtual screen plane 469, so that they have the samelight field coordinate u=0 at this virtual screen plane 469, as viewedby the observer. In other words, the angular light field coordinates ofthe holographic surface 488 are rearranged by the holographic relaysystem 460 comprised of the beam splitter 485 and curved mirror 482 informing the relayed holographic surface 489. To correct for this, theangular light field coordinates leaving the screen plane 498 of lightfield display 497 may be arranged in a compensated manner to achieve thedesired angular light field coordinates leaving the relayed virtualscreen plane 469. Another perhaps unwanted effect is that the normal tothe light field display surface 498, usually the light field angularcoordinate u=0, often defines an axis of symmetry for projected raysfrom the light field display surface 498. The light rays produced at u=0from the light field display 497, defining axes of symmetry from thelight field display surface 498, may be relayed to the virtual screenplane 469 with significant values of u (i.e. angle θ with the normal 496to the virtual screen plane 469 may vary), especially if the relayedholographic image is offset significantly from the optical axis 483.This may cause the field of view to be altered. In general, to minimizefield-of-view changes for holographic surfaces relayed by optical relaysystem shown in FIG. 4D, the light field display 497 may be centered sothat holographic surfaces such as 488 may relayed to positions 489 whichare as close as possible to the optical axis 483. In some embodiments,the focusing function of the mirror 482 shown in FIG. 4D may be replacedwith one or more optical elements such as lenses, mirrors, or somecombination of these elements. In one embodiment, the mirror 482 may bereplaced by the lens 444 and reflector 442 shown in FIG. 4E as discussedabove with respect to FIG. 4C. In another embodiment, the entire relaysystem 460 may be replaced with a relay formed of one or more lensessuch as the lens relay system 480 shown in FIG. 4F as discussed abovewith respect to FIG. 4C.

FIG. 5A shows an orthogonal view of a light field display and an idealholographic object relay system 103 which relays two holographic objectsprojected on either side of a light field display screen plane 1021 at afirst location and viewed to a first observer 1048, to two relayedholographic surfaces on either side of a virtual display screen 1022 ata second location and viewed by a second observer 1050. The light fielddisplay 1001 may output light along a set of projected light paths thatincludes light rays along projected light paths 1030Z that help formsurface 1015Z in front 1010 of light field display screen plane 1021,and light rays along projected light paths 1036Z that help form object1016A behind 1011 the screen plane 1021. Light paths 1035 are tracedpaths for the light rays 1036Z that originate at the light field displaysurface 1021, which in this example is collocated with the displayscreen plane. Under ideal circumstances, the relayed holographic objects1017A and 1017B on either side of virtual screen plane 1022 appear toobserver 1050 exactly as directly projected holographic objects 1015Zand 1016Z appear to observer 1048 in absence of any relay system 103. Inother words, the LF display 1001 and the relay system 103 should beconfigured so that light rays along relayed paths 1032A and 1028A whichform relayed holographic surfaces 1017A and 1018A, respectively, reachobserver 1050 in the same way that the corresponding light rays alongprojected paths 1030Z and 1036Z which form the directly projectedholographic surfaces 1015Z and 1016Z, respectively, reach observer 1048in the absence of any relay system 103. From FIGS. 1A, 1B and 3A, andthe discussion below, it will be clear that to generate the relayedholographic objects 1032A and 1028A using a practical implementation ofa relay system 103, the location, depth profile, and magnification ofprojected objects 1015Z and 1016Z may have to be adjusted from theirlocations shown in FIG. 5A, and the light field angular coordinates mayhave to be rearranged for each of these projected holographic sourceobjects 1015Z and 1016Z.

FIG. 5B shows an embodiment of a holographic display system similar tothe holographic display system of FIG. 1A. The holographic displaysystem of FIG. 5B includes a first display 1001, which may be a lightfield display configured to project light along a set of projected lightpaths 1030A and 1036A to form at least first and second holographicsurfaces 1015A and 1016A having first and second depth profiles relativeto a display screen plane 1021, respectively. The holographic displaysystem also includes a relay system 104 positioned to receive lightalong the set of projected light paths 1030A and 1036A from the lightfield display 1001 and relay the received light along a set of relayedlight paths 1032A and 1028A such that points on the first and secondprojected holographic surfaces 1015A and 1016A are relayed to relayedlocations that form first and second relayed holographic surfaces 1017Aand 1018A, having first and second relayed depth profiles relative to avirtual screen plane 1022, respectively.

FIG. 5B shows a holographic relay system 104 comprised of a beamsplitter 1005 and an image retroreflector 1006A. The light field display1001 may be similar to the light field display 1001 discussed aboverespect to FIGS. 1A, 1B, 3A and 5A. The light field display 1001projects out-of-screen holographic surface 1016A on the viewer side 1010of the screen plane 1021, and in-screen holographic surface 1015A on thedisplay side 1011 of the screen plane 1021. In an embodiment, the lightfield display 1001 may output light along a set of projected light pathsthat includes light rays along projected light paths 1036A that helpform surface 1016A, and light rays along projected light paths 1030Athat help form in-screen surface 1015A (paths 1033 are ray trace linesthat don't represent physical rays). Each of the set of projected lightpaths 1030A and 1036A has a set of positional coordinates (X,Y) andangular coordinates (U,V) in a four-dimensional (4D) coordinate systemdefined by the light field display. These light rays may diverge as theyapproach the beam splitter 1005. Some fraction of this incident light isreflected by the beam splitter 1005 toward the image retroreflector1006A along a set of reflected light paths that include paths 1037A fromthe incident light 1036A and paths 1031A from the incident light 1030A,while the remaining light 1034 not reflected by the beam splitter passesthrough the beam splitter along a set of transmitted light paths 1034and may be lost, not contributing to imaging of relayed holographicsurfaces 1017A and 1017B. The retroreflector 1006A may contain a finearray of individual reflectors, such as corner reflectors. Theretroreflector 1006A acts to reverse each ray of incident light paths1037A, 1031A in substantially the opposite direction from the approachdirection, with no significant spatial offset. Light rays alongreflected light paths 1037A reverse their direction upon reflecting fromthe beam splitter 1005, substantially retrace their approach angle toretroreflector 1006A, and some fraction of their intensities passthrough the beam splitter 1005 along relayed light paths 1028A,converging at the location 1018A of a holographic surface. In this way,holographic surface 1016A projected directly by the light field display1001 is relayed to form relayed holographic surface 1018A. Similarly,rays along light paths 1031A reverse their direction upon hitting thebeam splitter 1005, retrace their approach paths to retroreflector1006A, and some fraction of their intensities pass through the beamsplitter along relayed light paths 1032A, converging and formingholographic surface 1017A. In this way, holographic surface 1015Aprojected directly by the light field display 1001 is relayed to formholographic surface 1017A. The relayed light paths 1028A and 1032A makeup a set of relayed light paths that originated from the set ofprojected light paths from the display 1001 to the beam splitter 1005and then through the set of reflected light paths from the beam splitter1005 to the retroreflector 1006A. In an embodiment, each of the set ofrelayed light paths has a set of positional coordinates (X,Y) andangular coordinates (U,V) in a four-dimensional (4D) coordinate systemas defined by the relay system 104. In-screen surface 1015A, which isprojected at a greater depth than out-of-screen surface 1016A by thelight field display 1001, is relayed as surface 1017A, which is nowcloser to the viewer 1050 than surface 1018A relayed from 1016A. Inother words, the depth profile of holographic surfaces 1015A and 1016Aprojected by the light field display is reversed by the holographicrelay system 104. The vertical distance between holographic surface1016A and the beam splitter 1005 D1 is substantially the same as thehorizontal distance between the corresponding relayed holographicsurface 1018A and the beam splitter 1005. Similarly, the verticaldistance D2 between holographic surface 1015A and the beam splitter 1005is substantially the same as the horizontal distance D2 between therelayed surface 1017A and the beam splitter 1005. As discussed in regardto the optional optical element 1041A shown in FIG. 1B, the opticalelement 1041A is also an optional optical element. This 1041A may be aquarter wave retarder which may result in a majority of light rays alongpaths 1031A or 1037A returning to the beam splitter 1005 with a linearpolarization opposite from that of the light rays leaving the beamsplitter 1005, whereupon the majority of these light rays will bedirected toward the viewer 1050, rather than deflected by the beamsplitter 1005 and towards the display 1001. Also, the light ray alongpath 1042A of the projected light paths 1036A from holographic surface1016A, is projected from the light field display normal to the displayscreen plane 1021, and usually is assigned to the angular light fieldcoordinate value (u=, v)=(0, 0). This light ray produces light ray alongrelayed path 1042B, which helps form relayed holographic surface 1018A.For observer 1050, the light ray 1042B is projected normal to thevirtual display plane 1022, and will be perceived as a ray with lightfield angular coordinate(u, v)=(0, 0) to observer 1050. To furthergeneralize, the optical relay system 103 preserves the light ray atlight field coordinate (u, v)=(0, 0) to stay at that value, even afterbeing relayed, despite the required rearrangement of light field angularcoordinates that is shown in FIG. 2B to reverse depth with theretroreflector configuration shown in FIG. 5B. Alternatively, acorrective optical element may be included in the holographic displaysystem of FIG. 5B to reverse depth. In an embodiment, a correctiveoptical element 20 shown in FIG. 2A may be disposed in the set ofrelayed light paths 1028A and 1032A, and the corrective optical element20 is configured to reverse the polarity of the angular coordinates(U,V) of each of the set of relayed light paths such that a viewerperceiving the first and second relayed holographic surfaces 1017A,1018A through the corrective optical element 20 would perceive the acorrected depth order that is the same as the depth order of the firstand second holographic surfaces 1015A, 1016A. In an embodiment, thecorrective optical element 20 may be disposed in the virtual displayplane. In another embodiment, a corrective optical element 20 may bedisposed in the set of projected light paths 1030A, 1036A and opticallypreceding the relay system 104, and the corrective optical element 20may be configured to reverse the polarity of the angular coordinates(U,V) of each of the set of projected light paths 1030A, 1036A such thatthe first and second holographic surfaces 1015A and 1016A have apre-corrected depth order. In an embodiment, the corrective opticalelement 20 may be disposed in the display screen plane

FIG. 5C shows a light field display 1001 and a relay system 105 similarto the relay system 460 discussed above with respect to FIGS. 4C and 4D.In an embodiment, the holographic object volume relay 105 is comprisedof a beam splitter used to redirect diverging light from holographicsurfaces onto a concave reflective mirror 1007A which refocuses thisdiverging light into relayed holographic surfaces. Retroreflector 1006Ain FIG. 5B has been replaced with a concave reflective mirror 1007A inFIG. 5C. In the setup shown in FIG. 5C, in an embodiment, the mirror maybe a spherical mirror with a radius of curvature approximately equal tothe optical path length between the display screen plane 1021 and thesurface of the mirror, akin to the mirror center of curvature C′ 441 inFIG. 4D being located at or near the screen plane 468 in FIG. 4C. Thesame holographic surfaces 1015A and 1016A are projected by the lightfield display 1001 as shown in FIG. 5B along a set of projected lightpaths 1030A, 1036A. The set of projected light paths 1030A and 1036A maybe considered as determined according to a first four-dimensional (4D)function defined by the light field display 1001, such that eachprojected light path has a set of positional coordinates (X,Y) andangular coordinates (U,V) in a first 4D coordinate system defined withrespect to a display screen plane 1021. Light from holographic surface1015A reflects from the beam splitter 1005 into light rays alongreflected light paths 1031A, rather than being directed backwards alongtheir same path as they were with the retroreflector 1006A in FIG. 5B,these rays are reflected along relayed paths 1032B to converge and formholographic surface 1017B. The relayed holographic surface 1017B isslightly smaller than the source holographic surface 1015A, due tominification performed by the concave mirror corresponding to theoptical path length between holographic surface 1015A and the mirror. Inan embodiment, the mirror 1007A is a spherical mirror, and the pathlength between the holographic surface 1015A and the mirror 1007A isslightly larger than the radius of curvature of the surface of mirror1007A. Similarly, light from holographic surface 1016A reflects from thebeam splitter 1005 into light rays along reflected paths 1037A, butrather than being directed backwards along their same path as they werewith the retroreflector 1006A in FIG. 5B, these rays are reflected alongrelayed paths 1028B to converge and form holographic surface 1018B. Therelayed holographic surface 1018B is slightly larger than the sourceholographic surface 1016A, due to magnification performed by the concavemirror corresponding to the optical path length between holographicsurface 1015A and the mirror. In an embodiment, the mirror is aspherical mirror, and the path length between the holographic surface1016A and the mirror 1007A is slightly smaller than the radius ofcurvature of the surface of mirror 1007A. In addition, the depthordering of the holographic surfaces is conserved by the relay: thesource surface 1016A is projected to be in front of the screen plane1021, and its relayed surface 1018B is also projected in front ofvirtual screen plane 1022. The source surface 1015A is projected behindthe screen plane 1021, and its relayed surface 1017B is also projectedbehind the virtual screen plane 1022, further from the viewer in eachcase. Thus, the depth reversal that occurs with the retroreflector inFIG. 5B has been avoided by using the mirror 1007A. Finally, because animage generated by the concave mirror 1007A is flipped, the relayedholographic sphere 1018B is projected to a position beneath the relayedholographic box 1017B, in opposite order to the position of thesesurfaces that appears in FIG. 5B. The set of relayed light paths 1028B,1032B may be considered as having been determined according to a second4D function defined by the relay system 105, such that each relayedlight path has a set of positional coordinates (X,Y) and angularcoordinates (U,V) in a second 4D coordinate system defined with respectto a virtual screen plane 1022. The magnification, minification, andposition changes of the relayed surfaces 1018B and 1017B are all theeffect of the application of the second 4D function in the second 4Dcoordinate system.

In order to generate the relayed holographic surfaces shown in FIG. 5Bto a viewer 1050, some corrections may be made to the holographicsurfaces projected by the display shown in FIG. 5C. In an embodiment,the light field display 1001 may include a controller 190 configured toreceive instructions for accounting for the second 4D function byoperating the light field display 1001 to output projected lightaccording to the first 4D function such that the positional coordinatesand angular coordinates in the second 4D coordinate system for each ofthe set of relayed light paths 1028C and 1017C allow the relayedholographic surfaces 1018C and 1017C to be presented to a viewer asintended. FIG. 5D shows the position and magnification of theholographic surfaces that would have to be generated by the light fielddisplay 1001 if a relay system 105 with a curved mirror configurationshown in FIG. 5D is used. Holographic surface 1015A in FIG. 5C wouldhave to be projected to the position of holographic surface 1015C inFIG. 5D, and made slightly smaller to compensate for the magnificationthat results from the surface being a closer distance to the mirror.Holographic surface 1016A in FIG. 5C would have to be projected into theposition of holographic surface 1016C in FIG. 5D, and magnified tocompensate for the minification of the image that occurs at a greaterdistance from the mirror. The positions of holographic surfaces 1015Cand 1016C are right-left swapped, relative to 1015A and 1016A in FIG. 5Cto account for the inversion of the image that occurs with reflectiondue to the mirror. The result is that holographic surface 1015C isrelayed into 1017C, in precisely the same place as 1017A in FIG. 5B, andholographic surface 1016C is relayed into 1018C, in precisely the sameplace as 1018A in FIG. 5B.

In FIG. 5D, the group of light rays along projected light paths 1036Cwhich form the projected holographic sphere surface 1016C map to thegroup of light rays along relay light paths 1028C that form the relayedholographic surface 1018C. In a similar way, in FIG. 5B, the group oflight rays along projected light paths 1036A from the holographic spheresurface 1016A map to the group of light rays along relayed light paths1028A that form the relayed holographic surface 1018A. Upon closeinspection of FIG. 5B, the middle ray 1042A projected normal to thescreen plane 1021 (or display surface 1021) in FIG. 5B, often associatedwith a light field angular coordinate (u=, v)=(0, 0), maps to the middleray 1042B which is normal to the virtual screen plane 1022 viewed byviewer 1050. In other words, for the retroreflector configuration shownin FIG. 5B, the light ray produced at (u=, v)=(0, 0) is preserved,despite the fact that the angular coordinates u and v have to be swappedas shown in FIG. 2B to correct the reversal of depth. However, in thecurved mirror relay configuration shown in FIG. 5D, where no reversal ofdepth occurs, the center light ray 1042C in the group of projected lightrays 1036C projected normal to the screen plane 1021 of light fielddisplay 1001, often associated with a light field angular coordinate(u=, v)=(0, 0), maps to the middle ray 1042D which may not be normal tothe virtual screen plane 1022 viewed by viewer 1050. This is the samebehavior that is shown in FIG. 4D, where light rays 490C and 491Cprojected normal to the display surface 497 produce light rays 490E and491E, respectively, which generate angles θ₁ and θ₂ that vary withrespect to the normal to the virtual screen plane 469, depending in parton the location the rays intersect the holographic surface 488. Theresult is that the viewer will not see the correct light fieldinformation from the light ray 1043D. In the example that a specularhighlight is projected by the light field display 1001 in FIG. 5D alonglight ray along the projected light path 1042C, this specular highlightwill appear on mapped ray along the relayed light path 1042D at an angleto the normal of virtual screen plane 1022. To correct for this, thecolor and intensity information that is projected on (u=, v)=(0, 0) rayalong projected path 1042C in absence of relay system 106 should insteadbe projected on light ray along the projected path 1043C if the relaysystem 106 is in place so that this information will appear on mappedray along the relayed path 1043D, which is the (u=, v)=(0, 0) rayrelative to the virtual screen plane 1022 and the observer 1050. Inother words, some remapping of light field coordinates may be made onthe light field display 1001 (in addition to the magnificationadjustments previously described) in order to properly relay aholographic surface using a relay optical configuration with a curvedmirror 1007A.

Under the circumstance where the LF display 1001 produces unpolarizedlight, and an unpolarized 50% beam splitter 1005 is used, about half thelight from holographic surfaces 1015C and 1016C is lost upon the firstpass through the beam splitter 1005, and another half of the light islost upon the second pass through the beam splitter 1005, resulting inno more than 25% of the light from the holographic surfaces beingrelayed. If a polarized beam splitter 1005 is used, then it is possiblethat half of unpolarized light from the holographic surfaces 1015C and1016C is lost upon the first reflection from the beam splitter 1005, butthe remaining light directed toward the mirror 1007A will be in a knownfirst state of linear polarization. With a quarter wave retarder usedfor the optional optical element 1041A, the light returning from themirror may be mostly in a known second state of linear polarization,orthogonal to the first state, and mostly be transmitted through thepolarized beam splitter 1005, contributing to the relayed holographicsurfaces 1017C and 1018C. Under these circumstances, between 25% and 50%of the light from the holographic surfaces 1015C and 1016C may berelayed to holographic surfaces 1017C and 1018C. If the light fielddisplay 1001 produces polarized light, this efficiency can be increasedsubstantially with the use of a polarized beam splitter 1005 and aquarter wave retarder 1041A.

In FIG. 5D, half of the light from light paths 1036C or 1030C from theholographic surfaces 1016C or 1015C, respectively, may be wasted sinceit passes through the beam splitter 1005 into light rays alongtransmitted paths 1034 as shown in FIG. 5C. It is possible to addanother mirror 1007B, identical to mirror 1007A, placed opposite to thedisplay 1001A on the other side of the beam splitter 1005, andorthogonal to mirror 1007A. FIG. 5E is an orthogonal view of a lightfield display and a holographic relay system 107 comprised of a beamsplitter 1005 and two concave mirrors 1007A, 1007B placed orthogonallyto one another to achieve a high efficiency for light transmission fromprojected holographic surfaces to relayed holographic surfaces. Thisconfiguration is similar in concept to the second retroreflector 1006Bwhich appears in FIG. 1B. Light rays along the projected paths 1036Cfrom holographic surface 1016C either is reflected by the beam splitterinto reflected light paths 1037A directed toward the mirror 1007A, orpasses through the beam splitter into transmitted light paths 1042Adirected toward the mirror 1007B. Light paths 1037C directed towardmirror 1007A reflect into light paths which are again incident on thebeam splitter 1005, and a fraction of this light is transmitted throughto relayed paths 1028C (while the remaining fraction of this lightincident on the beam splitter 1005, not shown, is directed downward backtoward the light field display 1001). Light paths 1042A directed towardmirror 1007B reflect into light paths 1042B, which are incident on thebeam splitter 1005, and a fraction of this light is reflected into paths1028C, combining with the paths of light reflected by mirror 1007A(while the remaining fraction of this light, not shown, is transmittedthrough the beam splitter 1005 and directed back toward the light fielddisplay 1001). The same is true for light from holographic surface1015C, being relayed into holographic surface 1017C, but these lightpaths are not shown in FIG. 5D. In an embodiment, the concave mirrors1007A and 1007B and the beam splitter 1005 are aligned such that thelight along paths 1028C reflected from mirrors 1007A and 1007Bsubstantially overlap.

Under the circumstance where the LF display 1001 produces unpolarizedlight, and an unpolarized 50% beam splitter 1005 is used, almost all thelight from holographic surfaces 1015C and 1016C is directed to eithermirror 1007A or 1007B. Upon returning, at most half of the lightreflected from each mirror may be transmitted through the beam splitter1005 toward the display, and not contribute to imaging of relayedholographic surfaces 1016C or 1017C. This gives an upper limit of 50% ofefficiency for light from holographic surfaces 1015C and 1016C to berelayed to holographic surfaces 1017C and 1018C. However, using apolarization beam splitter as well as a quarter wave retarder as theoptional optical elements 1041A and 1041B, as described in thediscussion of FIG. 1A as well as FIG. 5D, a substantially higherefficiency may result, since most of the light directed toward eachmirror has a specific linear polarization which may be rotated by 90degrees on its return trip back toward the beam splitter, resulting inmost of the light of two different reflected polarizations beingrecombined as it is directed to the relayed holographic surfaces 1017Cand 1018C.

In some embodiments, the focusing function of the mirrors 1007A and1007B shown in FIGS. 5C-5E may be replaced with one or more opticalelements such as lenses, mirrors, or some combination of these elements.In one embodiment, the mirrors 1007A and 1007B may each be replaced bythe lens 444 and reflector 442 shown in FIG. 4E as discussed above withrespect to FIG. 4C. In another embodiment, the entire relay systems 105and 106 of FIGS. 5C-5D may be replaced with a relay formed of one ormore lenses such as the lens relay system 480 shown in FIG. 4F asdiscussed above with respect to FIG. 4C.

The relay 106 of the configuration shown in FIG. 5D may be used as oneor more of the relays in a holographic relay system comprised of tworelays, as shown in FIGS. 3B. In FIG. 3B, both of the relays 130 and 140may be replaced with relay systems 106, but in FIG. 3C, only relay 130may be replaced by relay 106, since relay 140 requires light to betransmitted in two different directions. In another embodiment, twosubstantially identical relays 106 are used in the holographic relaysystem configuration shown in FIG. 3B, and the effects of theminification, magnification, and rearranging of light field angularcoordinates (u, v) for the first relay 130 described above in referenceto FIG. 5D are at least partially reversed by the second relay 140.

FIG. 6 shows an embodiment of a system which relays holographic surfacesprojected by a light field display 1001 using a transmissive reflector1105. An example of element 1105 is a dihedral corner reflector array(DCRA), which is an optical imaging element composed of a plurality ofdihedral corner reflectors, which can be realized as a two thin layersof closely-spaced parallel mirror planes, oriented so the planes areorthogonal to one another as shown in FIG. 4A. Another example is acorner reflector micro mirror array. The light field display 1001 may besimilar to the light field display 1001 discussed above respect to FIG.1 . The light field display 1001 projects out-of-screen holographicsurface 1016A on the viewer side 1010 of the screen plane 1021, andin-screen holographic surface 1015A on the display side 1011 of thescreen plane 1021. The transmissive reflector 1105 is positioned toreceive light along the set of projected light paths 1030A, 1036A anddirect the received light along the set of relayed light paths 1032A,1028A. In an embodiment, each of the set of projected light paths 1030A,1036A has a set of positional coordinates (X,Y) and angular coordinates(U,V) in a four-dimensional (4D) coordinate system defined with respectto the display screen plane 1021. In an embodiment, the transmissivereflector 1105 internally reflects a portion of the received light amonga plurality of internal reflective surfaces 401, 402 of the transmissivereflector 1105 and output light along the set of relayed light paths1032A, 1028A towards a virtual screen plane 1022 in a first direction.In an embodiment, each light path in the set of relayed light paths1032A, 1028A has a unique set of positional coordinates (X,Y) andangular coordinates (U,V) in a four-dimensional (4D) coordinate systemdefined with respect to the virtual screen plane 1022. Further, in anembodiment, an external surface 430 of the transmissive reflector 1105reflects a second portion of the received light along a set of reflectedlight paths 1130, 1136 in a second direction opposite the firstdirection. In an embodiment, the set of reflected light paths 1130, 1136and the set of relayed light paths 1032A, 1028A are substantiallyaligned such that the first and second relayed holographic surfaces1015A, 1016A are perceived from the first and second directions to havethe same depth profile relative to the virtual screen plane 1022.

In an embodiment, projected light rays along the project light paths1036A that converge on the surface of holographic surface 1016, andprojected light rays along the projected light paths 1030A that convergeat in-screen holographic surface 1015A (see the ray trace lines 1033),all diverge as they approach the transmissive reflector 1105. Somefraction of incident light rays along the projected light paths 1036Areflect from the external surface 430 of 1105 into rays along reflectedlight paths 1136. The other portion of the incident light rays along theprojected light paths 1036A pass through the transmissive reflector1105, undergoing reflections, and exit as light rays along relayed lightpaths 1028, which converge to form the relayed holographic surface1018A. Similarly, some fraction of incident light rays along the projectlight paths 1030A reflect from the external surface 430 of transmissivereflector 1105 into light rays along reflected light paths 1130, whilethe other portion of incident light rays along the project light paths1030A are reflected within 1105 and emerge as converging light raysalong relayed light paths 1032A, forming relayed holographic surface1017A. Notice that projected surface 1015A, which was further from theviewer than projected surface 1016A, after being relayed as relayedsurface 1017A is now closer to the viewer after the holographic scenehas been relayed. The vertical distance between holographic surface1016A and the beam splitter D1 is substantially the same as thehorizontal distance between the relayed holographic surface 1018A andthe beam splitter 1105. Similarly, the vertical distance D2 betweenholographic surface 1015A and the beam splitter 1105 is substantiallythe same as the horizontal distance between the relayed surface 1017Aand the beam splitter 1105. An observer 1050 will see holographicsurface 1017A floating in space slightly in front of holographic surface1018A. An observer 1350 will see the reflected holographic surface 1018Aperceived to be at the convergence point of set of reflected light paths1136, and will see the reflected holographic surface 1015A perceived tobe at the convergence point of set of reflected light paths 1130.However, if the holographic source surfaces 1015A and 1016A are renderedprior to being displayed in order to achieve the correct depth orderingof relayed holographic surfaces 1017A and 1018A as observed by viewer1050, which means the depth of surfaces is reversed about the screenplane 1021 and the light field angular coordinates U-V are reversed asshown in FIGS. 2B and 2C, and discussed in reference to FIGS. 1A and 5Babove, then the U-V coordinates will be reversed for the surfacesreflected from the surface of transmissive reflector 1105 and observedat 1350. In other words, the depth may not appear correctly forholographic surface 1017A or 1018A for an observer 1350 viewing lightrays 1130 or 1136, respectively. To correct for this, it is possible toplace a correction optical element similar to that shown in FIG. 2A atthe plane 1137 in order to perform U-V coordinate reversal for the setof the reflected light paths 1130, 1136. In another embodiment, with adifferent light field rendering of holographic surfaces 1015A or 1016A,with no correction optical element at plane 1137, the observer 1350 mayperceive the holographic surfaces 1017A and 1018A with the correct depthordering, and a corrective optical element similar to that shown in FIG.2A may be placed at the virtual display plane 1022 as discussed abovewith respect to FIG. 5B to allow observer 1050 to also view theholographic surfaces 1017A and 1018A with the correct depth ordering. Inother words, if the correction optical element like that shown in FIG.2A is used to allow both observers 1050 and 1350 to see the holographicsurfaces 1017A and 1018A with the correct depth, they can be placed atplane 1022 or 1137, depending on whether the light field rendering ofholographic surfaces from the light field display 1001 contains stepswhich reverse the depth around the screen plane 1021 and reverse thepolarity of the U-V coordinates as shown in FIG. 2B.

FIGS. 7 illustrates a holographic system that is the same as theholographic system of FIGS. 5B with the addition of another display 1201opposite the first display 1001 and sandwiching the relay system 108,and the numerical labeling from FIG. 5B applies to FIG. 7 . The relaysystem 108 is comprised of a beam splitter 1205 and a retroreflector1006A. If 1201 is a light field display, then the light field display1201 may be configured as the light field display 1001 discussed abovewith respect to FIGS. 1A, with one or more display surfaces 1202,containing a plurality of light source locations, an imaging relay 1203which may or may not be present which acts to relay images from theemissive displays to an energy surface 1205, and an array of waveguides1204 which project each light source location on the energy surface intoa particular direction in three dimensional space. The energy surface1205 may be a seamless energy surface that has a combined resolutionthat is greater than any individual emissive display device 1202, whileplane 1221 is the screen plane of 1201. If 1201 is a traditional 2Ddisplay, then relays 1203 and/or waveguides 1204 may be absent. Display1201 may display a 2D image (not shown) or a holographic surface 1213.The rays along an additional set of projected light paths 1231 leavingthe display 1201 reflect off of the surface of the beam splitter 1205,forming diverging ray group along an additional set of relayed lightpaths 1233, which can be ray traced back through imaginary paths 1234 toreveal a convergence point at a perceived holographic surface 1214. Thevertical distance D3 between the displayed surface 1213 and the beamsplitter 1205 is substantially equal to the horizontal distance betweenthe beam splitter and the perceived surface 1214. An observer 1050 willsee holographic surfaces 1017A, 1018A, and displayed surface 1214 whichmay or may not be holographic depending on whether display 1201 is alight field display. Using a 2D display as 1201, it is possible tocreate a uniform background imaging plane that can be placed at anyreasonable distance from the observer 1050 depending on the distancebetween display 1201 and beam splitter 1205. A parallax element 1207 canbe placed in the path of display 1201 at distance 1210 from the screenplane of 1201 in order to block some or all of the light from display1201, and can take the form of a portion of a liquid crystal displaywithout a backlight, a transparent display, a real physical surface, orthe like. The parallax barrier 1207 can be used to block out portions ofthe surface 1214 in the event that holographic surface 1017A orholographic surface 1018A occludes 1214, and both images are not desiredto be displayed at the same time. If the parallax barrier 1207 is aportion of an LCD panel containing one or more polarizers and a liquidcrystal (LC) layer, the beam splitter can be a polarization beamsplitter that is selected to reflect 100% of the polarized light passingthrough 1207. Similarly, a parallax barrier 1208 can be placed abovelight field display 1001 at a distance 1211 in order to block all orsome of the light from display 1001, and can take the form of a portionof a liquid crystal display without a backlight, a transparent display,a real physical surface, etc. It is to be appreciated the variousembodiments in above discussions with respect to FIG. 7 may beimplemented in part or in whole in other embodiments of the holographicdisplay systems of the present disclosure, including those in FIGS.4C-4D and FIGS. 5C-5E. For example, the second display 1201 and parallaxelements 1207 and 1208 discussed above may be implemented to work with arelay system that includes at least one concave mirror as described inFIGS. 4C-4D and FIGS. 5C-5E.

Shown in FIG. 8A is a holographic system that is the same as theholographic system 110 of FIG. 6 with the addition of another display1201 opposite the first display 1001 and sandwiching the relay system109, and the numbering labelling from FIGS. 6 applies to FIGS. 8A. Ifdisplay 1201 is a light field display, then the light field display 1201may be configured as the light field display 1201 discussed above withrespect to FIGS. 7 . Display 1201 may display a 2D image (not shown) ora holographic surface 1213. The rays along an additional set ofprojected light paths 1231 leaving the display may partially reflect offof the surface of the transmissive reflector 1305, forming diverging raygroup along an additional set of relayed light paths 1332. Rays 1231 mayalso pass through the transmissive reflector 1305, undergoingreflections, and exit as light rays along a set of transmitted lightpaths 1333, which converge to form the relayed holographic surface 1314.The vertical distance D3 between the displayed surfaces 1213 and 1305may be substantially equal to the horizontal distance between surface1305 and the relayed holographic surface 1314. An observer 1050 will seeholographic surfaces 1017A, 1018A, and displayed surface 1314 which mayor may not be holographic depending on whether 1201 is a light fielddisplay. Using a 2D display as 1201, it is possible to create a uniformbackground imaging plane that can be placed at any reasonable distancefrom the observer 1050 depending on the distance between display 1201and transmissive reflector 1305. A parallax element 1207 can be placedin the path of display 1201 at distance 1210 from the screen plane of1201 in order to block some or all of the light from display 1201, andcan take the form of a portion of a liquid crystal display without abacklight, a transparent display, a real physical surface, or the like.The parallax element 1207 can be used to block out portions of thesurface 1314 in the event that holographic surface 1017A or holographicsurface 1018A occludes 1214, and both images are not desired to bedisplayed at the same time. Similarly, a parallax element 1208 can beplaced above light field display 1001 at a distance 1211 in order toblock all or some of the light from display 1001, and can take the formof a portion of a liquid crystal display without a backlight, atransparent display, a real physical surface, etc. The parallax elements1207 and 1208 may not be necessary to avoid occlusion problems if 1201is a light field display, since coordinated rendering of both of thelight field displays can be used to avoid occlusion. Normally, nothingwill be placed on intermediate plane 1137 or the virtual screen plane1337. However, corrective optical element 20 from FIG. 2A or similarconfigurations that reverse the polarity of the angular 4D light fieldcoordinates U, V may be placed at plane 1137 and not plane 1337, orplane 1337 and not plane 1137, or at both locations, or at none. Also,corrective optics 20 at planes 1337 and 1137 may both be moved closer orfurther away from the transmissive reflector 1305. Another option is tohave corrective optics 20 from FIG. 2A or similar configurations whichreverse the polarity of U, V coordinates placed just above the screenplane 1021 of the light field display 1001. Finally, system 130 can bebuilt using a mirror in place of transmissive reflector 1305, which mayresult in two independent views at observer 1050 on the left of 1305 andan observer located on the right of 1305 (not shown), where eachobserver would only be able to see holographic surfaces from a singledisplay. It is to be appreciated the various embodiments in abovediscussions with respect to FIG. 8A may be implemented in part or inwhole in other embodiments of the holographic display systems of thepresent disclosure, include those in FIGS. 4C-4D and FIGS. 5C-5E. Forexample, the additional display 1201 and parallax elements 1207 and 1208discussed above may be implemented to work with a relay system thatincludes at least one concave mirror as described in FIGS. 4C-4D andFIGS. 5C-5E.

FIG. 8B shows an embodiment using the parallax barrier in FIG. 8A toperform occlusion handling. The labels of FIG. 8A apply in this drawing.A portion 1367 of parallax barrier 1207 may be activated to block light1361 from one side of projected surface 1213. Only the orthogonal rays1362 from the surface 1213 are shown, and they partially reflect fromthe transmissive reflector 1305 into rays 1364 that reach the observer1050. The rays 1362 are partially transmitted by 1305 and exit into rays1363, which form the projected holographic surface 1366. Substantiallyno blocked light rays 1361 from the portion of the surface 1213 arevisible to observer 1050, corresponding to the blocked portion 1365 ofthe relayed holographic image 1366.

FIG. 8C shows an embodiment of system similar to that shown in FIG. 8A,with substantially all the rays of light that would reach an observer1350 on the right of transmissive reflector 1305, but omitting some ofthe light rays that would reach an observer on the left of 1305 (nowshown). The labels of FIG. 8A apply to this drawing. Observer 1350 willperceive the holographic surface 1018A through the diverging rays 1337reflected from 1305, and holographic surface 1017A through the divergingrays 1331 reflected from 1305. If the display 1201 is a holographicdisplay, then holographic surface 1213 will be relayed to holographicsurface 1314, and the observer 1350 will see 1314 in the foreground, andholographic surfaces 1017A and 1018A in the background. If the display1201 is a 2D display, then observer 1350 will see a flat foregroundimage, and holographic surfaces 1017A and 1018A in the background. Asdiscussed for FIG. 8A, if 1201 is a light field display, occlusionhandling may be done by coordinating the two light fields 1001 and 1201,or by using the parallax barriers 1207 and/or 1208. If 1201 is a 2Ddisplay, then occlusion handling may be done using the parallax barriers1207 and/or 1208.

FIG. 8D illustrates an embodiment showing an abstraction of the displaysystem shown in FIGS. 8A and 8B. Display 1001 projects holographicsurface 1016A which is relayed by transmissive reflector into surface1018A which an observer 1050 sees in front of 1305. Display 1201projects holographic surface 1213 which is relayed by 1305 into surface1314 which an observer 1050 sees behind transmissive reflector 1305. Anembodiment comprising partially or fully enclosed transmissive reflectorsurface 1305 may allow observers from all angles to see holographicsurfaces in an extended viewing volume.

FIG. 8E is an embodiment of system of FIG. 8D with a transmissivereflector 1605 having at least a partially enclosed transmissivereflector surface. In an embodiment, the reflector surface may have aconical geometry configured to allow observers from all angles to seeholographic surfaces in an extended viewing volume. Transmissivereflector 1605 may be a dihedral corner reflector array (DCRA), which isan optical imaging element composed of a plurality of dihedral cornerreflectors, which can be realized as a two thin layers of closely-spacedparallel mirror planes, oriented so the planes are orthogonal to oneanother as shown in FIG. 4A. Another example is a corner reflector micromirror array. Holographic surface 1213 is projected by light fielddisplay 1201, and is relayed by the transmissive cone-shaped reflectorto viewable location 1314. Similarly, 1016A is projected by display 1001and relayed to viewable surface 1018A. This configuration allows anarrangement of holographic surfaces to be projected and relayed tolocations on the outside of the holographic cone as well as inside, afull 360 degrees around the display. Multiple observers like the oneshown at 1050 are possible at multiple locations around the display. Inan embodiment, the conical surface of the transmissive reflector 1605may have an apex 1610 aligned with a center of the display 1001 or 1201.Occlusion handling can be done by coordinating the projection ofsurfaces from both displays 1201 and 1001, as discussed for FIGS. 8A and8C. The transmissive reflector 1605 can be a cone shape, as shown, aregular pyramid with four or more planar sides, custom shaped, and maybe fully or partially enclosed.

In an embodiment, the transmissive reflector may be configured to havean apex 1810 and a polygonal base 1815. For, example, FIG. 8Fillustrates an embodiment of system similar to that shown in FIG. 8Ewith a pyramid-shaped transmissive reflector surface 1805. In anembodiment, the apex 1810 of the transmissive reflector 1805 may bealigned with a center of the display 1001 or 1201.

While various embodiments in accordance with the principles disclosedherein have been described above, it should be understood that they havebeen presented by way of example only, and are not limiting. Thus, thebreadth and scope of the invention(s) should not be limited by any ofthe above-described exemplary embodiments, but should be defined only inaccordance with the claims and their equivalents issuing from thisdisclosure. Furthermore, the above advantages and features are providedin described embodiments, but shall not limit the application of suchissued claims to processes and structures accomplishing any or all ofthe above advantages.

It will be understood that the principal features of this disclosure canbe employed in various embodiments without departing from the scope ofthe disclosure. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, numerousequivalents to the specific procedures described herein. Suchequivalents are considered to be within the scope of this disclosure andare covered by the claims.

Additionally, the section headings herein are provided for consistencywith the suggestions under 37 CFR 1.77 or otherwise to provideorganizational cues. These headings shall not limit or characterize theinvention(s) set out in any claims that may issue from this disclosure.Specifically, and by way of example, although the headings refer to a“Field of Invention,” such claims should not be limited by the languageunder this heading to describe the so-called technical field. Further, adescription of technology in the “Background of the Invention” sectionis not to be construed as an admission that technology is prior art toany invention(s) in this disclosure. Neither is the “Summary” to beconsidered a characterization of the invention(s) set forth in issuedclaims. Furthermore, any reference in this disclosure to “invention” inthe singular should not be used to argue that there is only a singlepoint of novelty in this disclosure. Multiple inventions may be setforth according to the limitations of the multiple claims issuing fromthis disclosure, and such claims accordingly define the invention(s),and their equivalents, that are protected thereby. In all instances, thescope of such claims shall be considered on their own merits in light ofthis disclosure, but should not be constrained by the headings set forthherein.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more,” “at least one,”and “one or more than one.” The use of the term “or” in the claims isused to mean “and/or” unless explicitly indicated to refer toalternatives only or the alternatives are mutually exclusive, althoughthe disclosure supports a definition that refers to only alternativesand “and/or.” Throughout this application, the term “about” is used toindicate that a value includes the inherent variation of error for thedevice, the method being employed to determine the value, or thevariation that exists among the study subjects. In general, but subjectto the preceding discussion, a value herein that is modified by a wordof approximation such as “about” or “substantially” may vary from thestated value by at least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “includes” and “include”) or “containing”(and any form of containing, such as “contains” and “contain”) areinclusive or open-ended and do not exclude additional, unrecitedelements or method steps.

Words of comparison, measurement, and timing such as “at the time,”“equivalent,” “during,” “complete,” and the like should be understood tomean “substantially at the time,” “substantially equivalent,”“substantially during,” “substantially complete,” etc., where“substantially” means that such comparisons, measurements, and timingsare practicable to accomplish the implicitly or expressly stated desiredresult. Words relating to relative position of elements such as “near,”“proximate to,” and “adjacent to” shall mean sufficiently close to havea material effect upon the respective system element interactions. Otherwords of approximation similarly refer to a condition that when somodified is understood to not necessarily be absolute or perfect butwould be considered close enough to those of ordinary skill in the artto warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skilled in the art recognizethe modified feature as still having the required characteristics andcapabilities of the unmodified feature.

1. A holographic display system, comprising: a first display, comprisinga light field display configured to project light along a set ofprojected light paths to form at least a first holographic surfacehaving a first projected depth profile relative to a display screenplane; and a relay system positioned to receive light along the set ofprojected light paths from the light field display and relay thereceived light along a set of relayed light paths such that points onthe first holographic surface are relayed to relayed locations therebyforming a first relayed holographic surface having a first relayed depthprofile relative to a virtual screen plane, the first relayed depthprofile being different from the first projected depth profile; whereinthe light field display comprises a controller configured to receiveinstructions for accounting for the difference between the firstprojected depth profile and the first relayed depth profile by operatingthe light field display to output projected light such that the firstrelayed depth profile of the first relayed holographic object is thedepth profile intended for a viewer.
 2. The holographic display systemof claim 1, wherein the light field display is configured to project thefirst holographic surface as an in-screen holographic surface or anoff-screen holographic surface.
 3. (canceled)
 4. The holographic displaysystem of claim 1, wherein each of the set of projected light paths hasa set of positional coordinates and angular coordinates in afour-dimensional (4D) coordinate system, and the instruction received bythe controller comprises a reversal of the polarity of the angularcoordinates of the first holographic surfaces in the 4D coordinatesystem.
 5. The holographic display system of claim 1, wherein the set ofprojected light paths form a second holographic surface having a secondprojected depth profile relative to the display screen plane, and pointson the second holographic surface are relayed by the relay system torelayed locations that form a second relayed holographic surface havinga second relayed depth profile relative to the virtual screen plane.6.-23. (canceled)
 24. The holographic display system of claim 1, whereinthe virtual screen plane is oriented at a non-parallel or aperpendicular angle relative to the display screen plane of the lightfield display.
 25. (canceled)
 26. The holographic display system ofclaim 1, wherein the relay system comprises a transmissive reflectorpositioned to receive light along the set of projected light paths anddirect the received light along the set of relayed light paths.
 27. Theholographic display system of claim 26, wherein the transmissivereflector internally reflects a portion of the received light among aplurality of internal reflective surfaces of the transmissive reflectorand outputs light along the set of relayed light paths towards thevirtual screen plane in a first direction.
 28. The holographic displaysystem of claim 26, wherein the transmissive reflector internallyreflects a first portion of the received light among a plurality ofinternal reflective surfaces of the transmissive reflector and outputthe first portion of the received light along the set of relayed lightpaths towards the virtual screen plane in a first direction, and whereinan external surface of the transmissive reflector reflects a secondportion of the received light along a set of reflected light paths in asecond direction opposite the first direction.
 29. The holographicdisplay system of claim 28, wherein the set of reflected light paths andthe set of relayed light paths are substantially aligned such that thefirst relayed holographic surface is perceived from the first and seconddirections to have the same depth profile relative to the virtual screenplane.
 30. The holographic display system of claim 28, wherein eachlight path in the set of relayed light paths has a unique set ofpositional coordinates and angular coordinates in a four-dimensional(4D) coordinate system, and the holographic display system furthercomprises a corrective optical element positioned in a locationintersecting the set of relayed light paths or in a locationintersecting the set of reflected light paths, wherein the correctiveoptical element is configured to reverse the polarity of the angularcoordinates of light paths passing therethrough.
 31. The holographicdisplay system of claim 28, wherein each light path in the set ofrelayed light paths has a unique set of positional coordinates andangular coordinates in a four-dimensional (4D) coordinate system, andthe holographic display system further comprises first and secondcorrective optical element positioned in first and second locations,respectively, the first location intersecting the set of relayed lightpaths and the second location intersecting the set of reflected lightpaths, and wherein the first and second corrective optical elements areeach configured to reverse the polarity of the angular coordinates oflight paths passing therethrough.
 32. The holographic display system ofclaim 26, wherein the transmissive reflector comprises a dihedral cornerreflector array comprising a plurality of dihedral corner reflectors.33. The holographic display system of claim 32, wherein the dihedralcorner reflector array comprises two layers of reflective planes, thetwo layers being parallel but offset in a first dimension, and wherein,the direction of the reflective planes in one layer orientedorthogonally to the direction of the reflective planes in the otherlayer in a second dimension.
 34. The holographic display system of claim1, further comprising: a second display disposed substantiallyorthogonally with respect to the first display; and a beam splitterconfigured to receive light along the set of projected light paths fromthe first display and an additional set of projected light paths fromthe second display and direct the received light towards the relaysystem.
 35. The holographic display system of claim 34, wherein thesecond display comprises a light field display configured to project anadditional holographic surface, points on the additional holographicsurface are relayed by the relay system to relayed points therebyforming an additional relayed holographic surface having a depth profilerelative to an additional virtual screen plane.
 36. The holographicdisplay system of claim 35, wherein the virtual screen planecorresponding to the first display and the additional virtual screenplane corresponding to the second display are located such that twodistinct holographic volumes are created.
 37. The holographic displaysystem of claim 35, wherein the virtual screen plane corresponding tothe first display and the additional virtual screen plane correspondingto the second display are located such that one continuous holographicvolume is created, the one continuous holographic volume being largerthan individual holographic volumes associated with either virtualscreen planes.
 38. The holographic display system of claim 1, furthercomprising a second display opposite the first display, the relay systembeing disposed between the first and second displays, wherein the relaysystem is configured to receive light along an additional set ofprojected light paths from the second display and relay the receivedlight along an additional set of relayed light paths.
 39. Theholographic display system of claim 38, wherein the second displaycomprises a light field display configured to project an additionalholographic surface and points on the additional holographic surface arerelayed by the relay system to relayed points thereby forming anadditional relayed holographic surface having a depth profile relativeto the virtual screen plane.
 40. The holographic display system of claim39, further comprising a parallax element located in the set ofprojected light paths from either the first or second displays, andwherein the parallax element is operable to occlude at least a portionof the holographic surface formed along the set of projected light pathsof the respective display.
 41. The holographic display system of claim39, further comprising a parallax element located in each of the set ofprojected light paths from the first and second displays, and whereineach parallax element is operable to occlude at least a portion of theholographic surface formed along the respective set of projected lightpaths. 42.-102. (canceled)